FIG. 1 depicts a prior art inspection process 100. The inspection process 100 includes a modeling stage 110 which is generally carried out during a setup of a system. The modeling stage 110 is followed by an inspection stage 120.
Stage 110 includes acquiring images 112 and creating a model 114 (based on the acquired images). The model has, for each pixel of the model, minimal gray level values, maximal gray level values and typical gray level values.
Stage 120 includes retrieving the model 124, acquiring images of an article 122, and comparing (126) images of the article to images retrieved from the model generated during setup. The comparison 126 is followed by a decision stage 128 (deciding whether defects exist) that may generate a list of defects.
FIG. 2 illustrates a prior art model creation process 130. During setup, a set of images are collected (132) from multiple dies. These dies are selected either randomly or by the user. These images are used to create (134) a “golden image” of a die, where the golden image is preferably assumed to have no defects. Each pixel of the “golden image” consists (136) of a typical gray level value (“Typ”), Minimal gray level value (“Min”) and a Maximal Gray level value (“Max”). These three values may be used during inspection to determine the presence of defects while minimizing false defect detection.